[Plugin: Category Posts Widget] Don’t show child category posts

I had trying to figure out how to modify the plugin not to show posts in child categorys. I found query_posts(array('category__in' => array(§id))); code, but don’t no how to use that code in plugin.

So if somebody could help me with this? Or is there better way to do this?
I could use only that code and specify that in template, but it would be easier to use widgets.

Thanks.

http://wordpress.org/extend/plugins/category-posts/